1. Technical Field
The disclosure relates to an inkjet printer configured to perform printing by ejecting inks from inkjet heads to a print medium.
2. Related Art
There is a line inkjet printer which performs printing by ejecting inks from a fixed inkjet head to a sheet while transferring the sheet.
In a line inkjet printer capable of performing color printing by using multiple color inks, multiple inkjet heads configured to eject the respective color inks are arranged at intervals along a sheet transfer direction (sub-scanning direction). In color printing, the inkjet heads are driven such that the color inks ejected from the nozzles of the inkjet heads land on a transferred sheet to overlap one another for each pixel.
In the line inkjet printer, attachment positions of the inkjet heads may be misaligned from originally-designed positions. This misalignment causes deterioration in print quality.
In view of this, measures are taken to reduce the deterioration in print quality due to misalignment of the inkjet heads. Specifically, the measure for misalignment in a sub-scanning direction involves adjusting an ink ejection timing for each of the inkjet heads. Meanwhile, the measure for misalignment in a main scanning direction involves selecting nozzles for the same pixel in each of the inkjet heads so as to minimize misalignment of the nozzles for the same pixel in the main scanning direction.
A positional relationship among the inkjet heads (nozzles) needs to be obtained to take measures like those described above. Procedures for obtaining the positional relationship are as follows.
First, a predetermined pattern image is printed by using the inkjet heads. In this pattern image, dots of each of the color inks are formed in a predetermined pattern. After the printing, the printed image of the pattern image is scanned with a scanner and image data is generated. Then, the positions of the dots of each color are calculated by analyzing the image data. The positional relationship among the inkjet heads (nozzles) are thus obtained based on the positions of the dots of the colors.
An inkjet printer described in Japanese Unexamined Patent Application Publication No. 2009-286139 uses a colorless-transparent functional ink. For example, in some cases, the colorless-transparent functional ink is ejected to overlap the color inks to improve the color density and gloss of the printed sheet. Moreover, in some cases, the colorless-transparent functional ink is ejected to the sheet before the ejection of the color inks to promote fixing of the color inks. The function of such a functional ink varies depending on a formula for the functional ink.